INDIANAPOLIS — An Indiana Senate committee voted 8-4 Monday evening, along party lines, in favor of a proposed constitutional ban on gay marriage, setting up a Senate battle on the issue later this week.

The Rules Committee, comprised of Democratic and Republican Senate leaders and chaired by Senate President Pro Tem David Long, waded through three hours of often emotional testimony on House Joint Resolution 3, before advancing the measure.

Monday's vote now sets up a debate over whether the so-called "second sentence" of HJR 3, banning civil unions, will be reinserted by Senate lawmakers.

The House narrowly stripped the "second sentence" ban on civil unions on a bipartisan vote last month, amid concerns that it went too far, even for supporters of the gay marriage ban. But HJR 3 supporters have urgently called for the sentence to be restored in order to set up a November public vote on the issue.

Indiana's constitutional amendment process requires proposals be vetted in two consecutive biennial meetings of the General Assembly, then go before voters in order to be written into the constitution. But passing the ban without the second sentence would restart the clock, making the soonest any public vote could happen 2016.

The proposed ban won broad bipartisan support in 2011, sailing through the General Assembly with little notice during a year in which sweeping education changes and five-week walkout by House Democrats dominated the debate. But a strong coalition of opponents, led by some of the biggest players in the state's business and higher education communities, emerged as a powerful force this year.

Curt Smith, president of the Indiana Family Institute and one of the conservatives leading the charge in favor of HJR 3, argued the "second sentence" is needed to protect the state against legal challenges, should the proposed ban be adopted.

"It's not enough to just define marriage in an amendment like this. You have to defend marriage," Smith said. "That's the lesson from the courts."

One of the potentially most influential voices, Republican Gov. Mike Pence, has largely removed himself from the debate, saying he supports reinserting the "second sentence" but will not be talking about the issue again until after the 2014 session ends.

Supporters of the ban showed up at the Statehouse Monday in larger numbers, in part with the help of African American church leaders who have mobilized recently. But they were still outnumbered by opponents, wearing red clothes, as they have throughout the Statehouse fight, to signify their opposition.

Jennifer Fisher, a recruiter in Fort Wayne, asked lawmakers to consider the personal implications of the ban for gay couples raising a family. She noted that she and her partner, a police officer from Fort Wayne, would like to have children at some point, but their legal standing in Indiana puts her in risk of losing their children.

"If she is killed in the line of duty, someone could take away my family," she said.

The full Senate could take up debate on the marriage ban as soon as Thursday.